Boot Process in sort by Shirring Shukla
In sort boot process of linux OS ....
power on --> BIOS load into RAM --> BIOS moto is to load OS --> for that he perform POST inventry and calls CMOS to know boot order
---> after getting boot order BIOS load it whatever it finds in first sector of hdd into RAM this is what we called MBR
M ----------------------------- B ----------------------------------- R
<----------------------------- 512 bytes --------------------------->
+--------------BS------------+ +--------PT--------+ +----MN----+
446 64 2
M ------------------------------ B ----------------------------------- R
--> Exaine PT of MBR to know where is active partition (AP) -> Then BIOS load whatever it finds on BS of AP
--> BIOS then load 1SBL(1st satge boot loader) which were put there by anocanda during install time.
--> 1SBL gives CHS # of the /boot/boot.map to BIOS to load 2SBL(2st satge boot loader)
--> 2SBL examine the binary format of grub.conf and follows all instructions given there.
--> with the help of BIOS 2SBL loads Linux kernel vmlinuz-2.4.20-8 into the RAM
--> 2SBL uncompress kernal vmlinuz and filled it into ram waht we see in /proc dirr...
--> Now Linux Kernel is into RAM which is much powerfull than 2SBL and takes total control from it.
--> With the help of BIOS Kernal uncompresses the /boot/initrd-2.4.20-8.img to find filesystem driver.
-> Now HDd driver available and Kernel is into RAM
-> Now Kernel Load /sbin/init program into RAM.
-> /sbin/init* examines /etc/inittab and
1> run level (0-6 what ever is is defined) and run an script name
2> /etc/rc.d/rc.sysinit in a subshell of inittab shell
which calls /etc/sysconfig/network to load networking
and start various functions defined in /etc/init.d/functions
and Mounts all local filesystems from /etc/fstab and updates /etc/mtab
and now function of ec.sysinit ends
Short summary of what rc.sysinit does
===================================== in sort waht done by rc.sysinit
hostname
system logs
date and time
keyboard
system font
swap partitions
usb
file system checks
mount the filesystems read/write
=====================================
3> /etc/rc.d/rc { as a subshell }
/etc/rc.d/rc3.d/K*
/etc/rc.d/rc3.d/S* --> start & stop of services
/etc/rc.d/rc.local -->
--> shell inittab is active and by defaults there are 6 mingettys out of which all entered into sleep state
--- except 1
---> this mingetty then executes the /bin/login process and is then it put into sleep state by init
---> and we get promped for username & password
--> * /bin/login execs /usr/bin/passwd which challenges for passwd from
us which then does authentication and authorization using PAM
---> after Right username and password
---> mingetty then goes into zombie state and is killed by init
---> defined shell loads and we get our shell based command prompt:#$
# Faced any problem Feedback in above contact me
#============================Scratch=================================#
# AND Many More .....................Linux is Endless #
#========================== Hope you Liked IT ==========================#
# BOOT PROCESS-- BY Shirish Shukla #
# RHC Engineer 2010 #
# shirish.linux@gmail.com #
# shirishlinux.blogspot.com #
# "Give Respect To Time One Day At Right Time, Time Will Respect You" #
#===================================================================#
# TRy Hard theres nothing that are un-achievable by HARDdd-WORKkk #
#===================================================================#
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